One commercially available ion implantation system uses an ion source spaced from an implantation chamber where one or more workpieces are treated by ions from the source. An exit opening in an ion generation chamber allows ions to exit the source so they can be shaped, analyzed, and accelerated to form an ion beam. The ion beam is directed along an evacuated beam path to the ion implantation chamber where the ion beam strikes one or more workpieces, typically generally circular wafers. The energy of the ion beam is sufficient to cause ions which strike the wafers to penetrate those wafers in the implantation chamber. In a typical application of such a system the wafers are silicon wafers and the ions are used to "dope" the wafers to create a semiconductor material. Selective implantation with the use of masks and passivation layers allows an integrated circuit to be fabricated.
In a so-called medium current implanter, wafers are treated one at a time by placing them at an implant station and scanning an ion beam across a wafer surface along a controlled path. The scanning motion is applied by a scanning electrode that sets up an electrostatic field for deflecting the ions in the ion beam along controlled paths.
U.S. Pat. No. 5,373,164 to Benveniste, which issued from the United States Patent and Trademark Office on Dec. 13, 1994 concerns such a medium current implanter. An ion implanation system disclosed in the '164 patent includes structure to create a dipole field through which the ion beam passes. The strength and direction of the dipole field is controlled to adjust an angle of impact between the workpiece, typically a silicon wafer and the ion beam. A side-to-side scanning motion is used to provide controlled doping of an entire silicon wafer.
The technique disclosed in the '164 patent will not work for controlled deflection of the ion beam used to treat multiple wafers used with a high current implanter. Such an implanter is disclosed in U.S. Pat. No. 5,554,857 which is assigned to Eaton Corporation and which is incorporated herein by reference. Electric scanning such as the scanning disclosed in the '164 patent is not suitable since the electric field used to produce the side to side scanning tends to de-stabilize the background neutralization that allows high current beam transport.